Michael Daly wrote:
wrote:

Given our lack of storage space, I am considering shortening them.

Sell them and buy the kayaks you want. I modify kayaks all the time,
but shortening the hull is just a waste of time and money.

Mike
Agreed as well. Assuming you get the right materials to effect the
repairs, there will still potentially be weaker spots and definitely
make a heavier (and probably quite ugly) boat.
Spiff them up, toss a coat of gelgloss on them, and sell them. Then buy
boats you can store and are usable as they were built.

Marsh

Cutting a piece out of the middle of the hull should be no great
challenge. Just be careful to choose the locations of the joined halves
that they match exaclty. Then sand off the inner surface around the cut
and apply a couple of layers of fibreglass soaked in resin through the
cockpit. Boat builders call it a "butt" join. I've used it in plywood
boats. While the boat is in pieces it should be easy to prepare the
inside, move the foot braces, etc.

The challenge would come in enlarging the cockpit. I don't see how you
can cut a piece out of the middle of a kayak without effecting the
cockpit, and they tend to have moulded coamings to keep out the water
and to allow a spray skirt to be tied on. Before cutting I'd want to
figure out what to do about the cockpit.

Wm Watt wrote:
Cutting a piece out of the middle of the hull should be no great
challenge. Just be careful to choose the locations of the joined halves
that they match exaclty.

How many boats have you seen that have the exact same hull profile
forward and aft of the centerline? Not many are designed that way.

Then sand off the inner surface around the cut
and apply a couple of layers of fibreglass soaked in resin through the
cockpit. Boat builders call it a "butt" join. I've used it in plywood
boats. While the boat is in pieces it should be easy to prepare the
inside, move the foot braces, etc.

That wouldn't be anywhere near strong enough. To do it right, you need
the inner glass, but you also need to feather the joint back a couple of
inches on the outside, lay in new glass to build the joint up to the
original thickness, then apply new gelcoat.

The challenge would come in enlarging the cockpit. I don't see how you
can cut a piece out of the middle of a kayak without effecting the
cockpit, and they tend to have moulded coamings to keep out the water
and to allow a spray skirt to be tied on. Before cutting I'd want to
figure out what to do about the cockpit.

The only feasible thing to do would be to remove the coaming first, then
enlarge the cockpit opening to the proper size after the boat is
shortened. If the cockpit is recessed or the shape of the deck changes
significantly, it will take a LOT of work to reinstall the coaming.

The bottom line is that this project simply isn't practical.

This idea of cutting a Kayak to size seems a bit dumb. Why don't you
just build a bigger storage space? Or if you want to work on a kayak
buy a stitch and glue kit for a smaller Yak. But if you insist on
cutting the kayak. Perhaps put in a 2 sturdy bulkheads about a 1 mm (or
less) apart and cut between them creating two water tight sections that
you can reconnect by butting the bulkheads together and bolting them
firmly in place. You might even want to have 3 reattach-able sections
stern cockpit and bow.

Thanks everyone for your ideas!

I'll let you know what happens!

Regards,

Nick

wrote:
This idea of cutting a Kayak to size seems a bit dumb. Why don't you
just build a bigger storage space? Or if you want to work on a kayak
buy a stitch and glue kit for a smaller Yak. But if you insist on
cutting the kayak. Perhaps put in a 2 sturdy bulkheads about a 1 mm (or
less) apart and cut between them creating two water tight sections that
you can reconnect by butting the bulkheads together and bolting them
firmly in place. You might even want to have 3 reattach-able sections
stern cockpit and bow.

Converting these to multi-piece kayaks is the only sensible solution
other than getting rid of them and buying appropriate boats.

Brian Nystrom wrote:

How many boats have you seen that have the exact same hull profile
forward and aft of the centerline? Not many are designed that way.

"Exact same profile" not required, just at a single point. How many do
you want? These are 20 year old craft. The model names have been posted
so you are welcome to look them up and let us know. Not many are
designed symetrical fore-and-aft today but at one time all canoes and
kayaks were symetrical. The many ways designers use to keep selling
more boats is a topic for another discussion.

Say they are not symetrical. Then the front section can be inserted
into the rear section and locating the cutting lines is not as
critical. Asymetrical would be easier.


That wouldn't be anywhere near strong enough. To do it right, you need
the inner glass, but you also need to feather the joint back a couple of
inches on the outside, lay in new glass to build the joint up to the
original thickness, then apply new gelcoat.

It may or may not be strong enough in a patch or a scarphed panel but
this is a tube. Any tension on one side is compensated by equal tension
on the other. Just sand off the inside surface, position the two
halves, cellotape around the outside to keep the resin from oozing out,
and glasstape the inside. No need to do any fancy finish work to the
outside. One does need, however to cut the hull carefully so the two
pieces fit.
People have reported using single sided taped butt joins on plywood
boats to avoid the problem of finishing the outside surface. Apparently
it does actually work there.



The bottom line is that this project simply isn't practical.

Where does practicallity enter into the hobby of paddling or
boatbuilding?
Giving up a day's pay to drive 200 miles to paddle down a river is
practical?
My own boatbulding is motivated as much by curiosity as practicality.
Can it be done?
Some don't like to spend money but time is no problem.

Wm Watt wrote:

at one time all canoes and kayaks were symetrical.

Care to back that up with something resembling a fact.

It may or may not be strong enough in a patch or a scarphed panel but
this is a tube. Any tension on one side is compensated by equal tension
on the other.

You really don't understand what a hull does in the real world. Tension has to
be balanced by compression. Local loads have to be accommodated, not just
overall bending moments.

Mike

Michael Daly wrote:
Wm Watt wrote:

at one time all canoes and kayaks were symetrical.

Care to back that up with something resembling a fact.

Moreover, at one time all river kayaks were not only symetrical but
were a standard 13 feet long. It wasn't until computer programs became
available that all the different shapes appeared.


It may or may not be strong enough in a patch or a scarphed panel but
this is a tube. Any tension on one side is compensated by equal tension
on the other.

You really don't understand what a hull does in the real world. Tension has to
be balanced by compression. Local loads have to be accommodated, not just
overall bending moments.

Any tension on one side is compensated by compression on the other.


Mike

Wm Watt wrote:
Michael Daly wrote:
Wm Watt wrote:

at one time all canoes and kayaks were symetrical.
Care to back that up with something resembling a fact.

Moreover, at one time all river kayaks were not only symetrical but
were a standard 13 feet long. It wasn't until computer programs became
available that all the different shapes appeared.

A look at Charlie Walbridge's old book on whitewater kayak making proves this to
be nothing but bull****. It also doesn't address sea kayaks and recreational
kayaks.

To this day, there are people designing kayaks without computer programs. It
ain't rocket science.

Any tension on one side is compensated by compression on the other.

Glad you sorted that out.

If you only reinforce on one side, as Brian pointed out, you'll get a weak
joint. Hull-to-deck seams on some cheaper sea kayaks are only taped on the
inside and are known to have split. No one I know would trust a one-sided seam
for strength.

Mike